To make bullets spin so they fly straight.
Long barreled gun, with grooves on the inside of barrel- is a rifle. Shorter version is a carbine. Handguns, such as pistols and revolvers also have grooved barrels.
Barrels have lands and grooves, not ammunition.
Smooth bores are bores or barrels in guns that do not contain rifling. Rifling is made up of lands and grooves that cause the bullet to turn within the barrel of the gun. This turning gives the bullet and gun its accuracy. A smooth bore gun is much less accurate than a rifled bore gun.
The barrel is straight. However, there are spiral grooves cut on the inside of the barrels. These spiral grooves, called rifling, make the bullet spin when it is fired. Just as a thrown football spins for an accurate throw, the spinning bullet makes for an accurate shot.
Gatling gun
on the muzzle end of the barrel there will be 3 grooves for the handgaurd/extension, if the barrel is smooth on the outside with no grooves it is a riot gun.
Lands and grooves.
Grooves
Grooves on inside of the barrel= a RIFLED firearm- the grooves are known as rifling. Grooves on the outside of the barrel= fluting, done to reduce weight
Rifling will leave grooves--impression in a bullet. These grooves can indicate the manufacturer of the gun that fired that bullet, AND, if there is a suspected gun in particular, microscopic variations can be used to confirm or refute that gun's involvement to a high degree of certainty.
Grooves cut into the inside of a gun barrel for the purpose of spinning the bullet when fired.
The original Gatling gun had six to ten barrels which rotated and fired independently. This was one of the earliest machine guns made.